This invention relates to regenerative furnaces and their operation, and in particular to the type of regenerative furnace commonly employed in the manufacture of flat glass. The invention particularly concerns the control of flow of gases through the flues to and from the checker packing material of the regenerators.
1. Field of the Invention
Because side fired flat glass furnaces typically include a relatively large number of burner ports (usually about four to eight on each side) spaced several feet apart from one another, the length of a regenerator bed associated therewith usually has a length which is several times greater than its width. And because of construction expediencies, the main flue carrying gases to and from each regenerator is usually located at one end of the regenerator. This arrangement unfortunately sets up lateral flow in the upper plenum and therefore an uneven flow distribution in the regenerator packing during the exhaust cycle, which has been found to cause the portion of the packing near the flue to become hotter than other portions of the packing. This localized overheating may often be reinforced in the subsequent firing cycle, during which the flow of incoming air has been detected favoring the end of the packing away from the flue so that the flue end is cooled less than the remainder of the packing. As a result, the flue end portion of the packing tends to deteriorate faster than others, thereby shortening furnace life. Furthermore, because the stored heat is concentrated in one portion of the packing, the efficiency with which air is preheated in the firing cycle is reduced. It is an object of the present invention to overcome these disadvantages.
2. Prior Art
U.S. Pat. Nos. 1,836,412 and 2,813,708 relate to modifying the flow patterns in regenerators. Both employ rigid baffles designed primarily for the purpose of rendering the air flow through the checker packing more uniform during the firing cycle. It is not apparent, however, how such arrangements could sufficiently influence flow in the opposite direction through the packing during the exhaust cycle to avoid concentrating heat at the flue end of the packing. Moreover, such baffle arrangements could change the gas flow pattern in the space beneath the packing during the exhaust cycle, thereby promoting lateral flow of the exhaust gases along the plenum above the packing and then into the packing at the flue end.
In U.S. Pat. No. 4,047,560 to Tsai it has been suggested that the difficulty of overheating of the upstream portion of the packing of the regenerator be minimized by the use of a movable baffle beneath the packing near the flue entrance to the regenerator. The baffle would deflect a substantial portion of the incoming airflow during the firing cycle into the portion of checker packing nearest the flue and thereby preferentially cool that portion. When the cycle is reversed, the baffle would be retracted so as to not interfere with normal gas flow pattern. Since the flue end of the packing will thereby have been cooled more than other portions during the firing cycle, the subsequent uneven flow of the exhaust gases will not cause an excessively unbalanced temperature raise at the flue end. Thus the inordinate concentration of the heat at the flue end is reduced and thermoenergy more efficiently utilized. It is also suggested in U.S. Pat. No. 4,047,560 that baffles would also be placed in the plenum above the packing so as to discourage lateral flow along the plenum during the exhaust cycle thereby alleviating the channeling of the exhaust gases to the packing of the flue end. The baffles in the plenum would be permanent. The construction utilizing a movable baffle while effective in minimizing the problem of overheating of the upstream checker portion does not completely effectively make possible the utilization of the maximum heat exchange capacity of the entire checker system. Further baffles in the upper plenum while restricting somewhat the flow of gases in the plenum also limit the firing arrangements which may be effectively made in the furnace as the air supplied to the burners is limited by the plenum baffles. Another disadvantage of the system of U.S. Pat. No. 4,047,560 is that the movable baffle requiring adjustment for each change of firing cycle presents a difficult materials usage in view of the size of the plate which must be moved and the reducing and oxidizing atmospheres to which it is subjected. Further, failure of the moving mechanism can create difficulties in overheating of the checkers in certain portions.
Therefore, there remains a need for a regenerator design which will provide even high temperature heating of the regenerator checkers for maximum heat recovery. As set forth above the flow over the checkers is not uniform. Therefore, less heat may be recovered from the downstream checkers than the upstream checkers as the temperature of these checkers is less. There remains a need for a flue design that would allow maximum recovery of regenerator heat and at the same time eliminate the possibility of over heating portions of the checker system. Further, there is a need for flue design which would not be blocked by a collapse of an arch holding the checker packing above the flue.